The present invention relates to seal assemblies for bearings, and more particularly to seal assemblies including an annular seal member secured at its outer periphery to the inner periphery of one end of the outer ring of an anti-friction bearing and having an inner peripheral seal lip part of which is lightly in contact with the inner ring.
Seals for anti-friction bearings must have high sealing properties while rendering the inner or outer ring rotatable by the lowest possible starting torque.
For this purpose, Japanese Utility Model Publication No. 20002/1964, for example, proposes a seal structure in which radial and axial labyrinths are combined to provide a clearance of increased length between the inner ring and the seal lip of an annular seal member. Thus the proposal contemplates an improved sealing function afforded by the complexity of the structure.
A seal assembly of another structure has been proposed and introduced into use as disclosed, for example, in the specification of U.S. Pat. No. 3,113,814. With reference to FIG. 1(a) showing the seal assembly, an annular seal member B has a seal lip which is positioned in a peripheral groove formed in the shoulder of an inner ring A, the seal lip being held out of contact with the grooved portion to provide a continuous labyrinth clearance extending radially and axially of the inner ring B.
Generally, anti-friction bearings such as deep groove ball bearings have a very great axial clearance which is five to ten times as large as the radial clearance thereof. To give an improved sealing function to a sealing assembly such as one shown in FIG. 1(a), the axial clearance between the grooved portion of the inner ring A and the seal lip must be minimized, but since the axial clearance of the bearing is very great as stated above, the seal lip will contact the side face of the grooved portion during the rotation of the bearing, if the axial clearance therebetween is reduced. Such contact will result in an abrupt increase in the rotation torque of the bearing, consequently leading to a marked rise in the temperature of the bearing and to increased wear of the seal lip. The rise of temperature will reduce the consistency of the grease or like lubricant enclosed in the bearing, rendering the lubricant more susceptible to leak.
To eliminate such drawbacks, the axial clearance between the side face of the grooved portion of the inner ring A and the seal lip may be made greater than the axial clearance of the bearing, but the labyrinth will then have a greatly reduced function, failing to prevent leakage of the lubricant and to exclude water, dust or like foreign matter. Thus, the seal lip will not be satisfactorily serviceable. The axial clearance of the bearing varies with the magnitude and direction of the load on the bearing. Further since the axial clearance between the seal lip and the side face of the inner ring grooved portion varies with the dimensional accuracy and assembly accuracy of the inner ring and of the seal, it is extremely difficult to properly adjust the clearance, and the seal is not always mountable in place. Seal assemblies of the non-contact type such as one shown in FIG. 1(a) therefore have inevitable drawbacks described above.
Accordingly when especially high sealing properties are required, sealing assemblies of the contact type are used, in which the inner peripheral seal lip of an annular seal member is entirely or partially adapted for sliding contact with part of the inner ring, as disclosed in the specifications of U.S. Pat. No. 3,245,735 and U.S. Pat. No. 2,310,607, etc. FIG. 1(b) shows a seal assembly of the contact type disclosed in the specification of British Pat. No. 1,181,045. It is seen that the lip of a seal ring B' has a relatively short radial length and a large width and therefore has high rigidity, failing to fully follow the axial displacement especially of the inner ring A'. Thus even the slightest increase in contact, when resulting from a relative axial displacement between the inner and outer rings or from reduced accuracy involved in mounting the seal ring, will entail an increase in the rotation torque of the bearing or an increase in the bearing temperature. The seal assemblies of this type are usable only for a greatly limited range of applications in which these drawbacks are justifiable.
On the other hand, bearings have found increasing use and are used with increasing frequency at high speeds in recent years. In fact, there is a growing demand for anti-friction bearings incorporating seal means which is outstanding in sealing properties and durability and which assures high rotation performance of the bearing. However, conventional seal assemblies of the non-contact type as well as of the contact type described above are unable to fulfil all of these requirements because of their inherent drawbacks. Additionally, the seal assemblies must be adapted for effective exclusion of foreign matter.